1. Field of the Invention
This invention relates to the processing of hydrocarbonaceous materials and more particularly it concerns the hydrogenation of these materials which contain solid material in the form of fines and the removal thereof in the course of the hydrogenation process.
2. Description of the Prior Art
It is known to produce hydrocarbonaceous materials such as oils, tars and waxes from the pyrolysis of coal and shale and from the extraction of tar sands. Hydrocarbonaceous materials which are produced in this manner, however, are not useful for most applications without further processing. This further processing usually involves hydrogenation, i.e., subjecting the hydrocarbonaceous material to hydrogen gas at high pressure and high temperature in the presence of a solid catalyst such as a metal salt or oxide. The hydrogenation process serves to break down the larger heavier organic molecules in the hydrocarbonaceous material by displacement of atoms of oxygen, nitrogen and sulfur (known as "hetero atoms") which link together sub-molecules. The displacement of these hetero atoms results in the production of mixtures of lighter weight lower viscosity and lower boiling point oils which can be separated from each other by fractionation.
In general, the aforesaid hydrogenation takes place in a heavy wall reactor which is maintained at a high pressure, e.g., 1000 to 10,000 pounds per square inch (70 to 700 kilograms per square centimeter). The reactor contains one or more beds of granulated catalyst material and the hydrocarbonaceous material and hydrogen gas together are passed through these beds. Some reactors are known as a fixed bed type and in those reactors the feed and hydrogen gas flow downwardly through each bed. Other reactors are known as the fluidized or ebullating bed type and in those reactors the feed and hydrogen gas flow upwardly through the catalyst material at sufficient velocity to maintain the individual catalyst particles in a state of suspension. Ebullating bed type reactors suitable herein are those used for processing oil which has been extracted from slurrys of coal shown and described in U.S. Pat. Nos. Re. 25,770, 3,321,393, 3,519,553, 3,519,555, 3,594,305 and 3,679,573. The fixed bed type of reactor permits the incorporation of several beds in a single housing so that successive stages of reaction can be carried out economically. The ebullating bed reactor, on the other hand, permits better contact between the feed, the hydrogen and the catalyst. Furthermore, the ebullating bed reactor is less susceptible to plugging or clogging by the accumulation of small particles of solid material, i.e. "fines" which are carried into the reactor with the incoming hydrocarbonaceous feedstock.
The prior art has failed to provide a satisfactory technique for removing fines from hydrocarbonaceous products. This is a serious problem in the processing of such materials produced from the pyrolysis of coal and shale or which have been extracted from tar sands, the materials normally contain two to five percent or more of fines. These fines can plug a fixed bed reactor. Also, because of vaporization which occurs in the course of operation of both fixed and ebullating bed reactors the fines concentration in the remaining liquid increases substantially so that plugging can become a problem in each type of reactor. In addition, unless the fines are eventually removed the resulting product oil will be unsuitable for most applications.
It is not practical to remove fines from coal pyrolysis or tar sands oil prior to hydrogenation because at this point the hydrocarbonaceous material is so thick and viscous that the fines cannot be segregated. Furthermore, the removal of fines from the hydrogenated product has not proven satisfactory because such removal requires small pore filters which clog very quickly and which must be replaced at frequent intervals.
It is, of course, known that solids may be separated from liquids by vaporizing the liquid, conducting the vapors to a different location and condensing the vapors. This technique, however, cannot readily be carried out prior to hydrogenation because the boiling point of many of the constituents of the coal pyrolysis oil is very high. On the other hand, although vaporization does occur during the hydrogenation process itself, the fines which are separated in the hydrogenation reactor will accumulate therein and will eventually clog the reactor.